setup.py: add test dependencies via "extras" (#66)

README.md

@@ -123,6 +123,18 @@ only linters and the ones you have already installed on your machine:
 $ tox -e flake8,pylint,bandit,py27,py36
 ```
 
+Or just install project in developer mode with test dependencies:
+
+``` bash
+$ pip install -e path/to/PySnooper[tests]
+```
+
+And run tests:
+
+``` bash
+$ pytest
+```
+
 Tests should pass before you push your code. They will be run again on Travis CI.
 
 # License #

setup.py

@@ -22,6 +22,12 @@ setuptools.setup(
     url='https://github.com/cool-RR/PySnooper',
     packages=setuptools.find_packages(exclude=['tests']),
     install_requires=read_file('requirements.in'),
+    extras_require={
+        'tests': {
+            'pytest',
+            'python-toolbox',
+        },
+    },
     classifiers=[
         'Environment :: Console',
         'Intended Audience :: Developers',